As a sparingly inflammable formed article of a porous cross-linked polymer containing a large volume of water, the cured article of a water-in-oil type emulsion containing up to 90% of an inner water phase has been known (British Patent No. 1,458,203, JP-A-47-29,479, and JP-A-48-94,785).
As an application of this water-in-oil type emulsion, JP-A-57-198,713 discloses a low-density porous polymer. This polymer is known to be capable of absorbing such a hydrophobic liquid as oil in the pores thereof. JP- A-60-217,204 and JP-A-60-217,205 disclose low-density modified polystyrene porous cross-linked polymers having a density of less than 0.2 g/cm.sup.3. These polymers are known to be capable of absorbing oil and water in the pores thereof, depending on the degree of modification. Besides, JP-A-62-250,002 discloses a knowledge that a low-density porous cross-linked polymer possessing elasticity is obtained by polymerizing an emulsion of a corresponding monomer while controlling the diameter of discontinuous phase liquid drops in the emulsion within a specific range.
The polymers which are disclosed in the aforementioned publications known to the prior art, however, are low-density porous polymers and contain a large volume of air in the pores which are distributed throughout their whole volume. To absorb a liquid, therefore, they require to exchange the large volume of air contained therein for the liquid. Owing to this exchange, they do not manifest any ability to absorb the liquid quickly. Further, these polymers suffer their pores to grow-in diameter while they are in the process of retaining the absorbed liquid in the pores, they readily release the absorbed liquid when they are exposed to pressure. Thus, these polymers exhibit only a poor liquid retaining power under load.
The elastic porous cross-linked polymer which is disclosed in JP-A-62-250,002 has a large pore diameter and a large porosity and assumes a spongy texture under normal conditions. If it is elected to be used as a liquid absorbable material, it will fail the service required of the liquid absorbable material unless it is improved in its own wettability with a liquid to be absorbed. It further manifests only an insufficient liquid retaining power under load and betrays deficiency in the liquid absorbing property. If the porous polymer in such a spongy texture as described above is mechanically compressed and converted into a formed article compact under normal conditions, it is no longer capable of absorbing liquid because the pores therein succumb to fracture under load of the mechanical compression. A porous polymer is generally such that when it gains in density, it is normally assumed to undergo compaction of the kind required of a liquid absorbable material. None of the liquid absorbable materials heretofore introduced to the art proves capable of absorbing a varying kind of liquid quickly at a high ratio of expansion on contact therewith.
Thus, the appearance of a compact liquid absorbable material which, on contact with a liquid such as water, alcohol, or petroleum, quickly absorbs the liquid into the interior thereof and expands with the absorbed liquid has been earnestly desired.
The present invention is aimed at fulfilling this desire. An object of this invention, therefore, is to provide a novel liquid absorbable material which is compact in a dry state and which, on contact with a liquid such as water, alcohol, or petroleum, quickly absorbs the liquid in the interior thereof and expands with the absorbed liquid. Another object of the present invention is to provide a method for attaining the production of this liquid absorbable material easily and conveniently.